Detroit 14L Pressure Relief Valve and Lose of Prime

Discussion in 'Freightliner Forum' started by J3DIKing, Nov 29, 2023.

  1. J3DIKing

    J3DIKing Bobtail Member

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    Nov 13, 2023
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    Hello community,

    As the title states these are the few issues I'm currently having.
    I've recently had an overhaul on my series 60 14L and only put a few miles on it from the shop to the house and is currently sitting.
    Every so often I'd start the truck and let it idle for a bit but I've experienced a couple minor issues.

    The truck seems to loose prime and wont start on its own but will with starting fluid. I've replaced the Fuel Check Valve to no avail, issue still stands.

    In addition to that while the truck is idling it's not purging air from the dryer before and after replacing the dryer and governor. I pulled the line from the compressor to the dryer and felt a good amount of pressure and no oil shooting out.

    Lastly once the truck is turned off I hear an air leak coming from the relief valve on top of the compressor the one next to the unloader valve and according to Bendix this is what is says verbatim from the manual.

    "All Bendix® BA-921® compressors are equipped with a safety valve to protect the compressor head in the event of, for example, a discharge line blockage downstream of the compressor. Excessive air pressure will cause the safety valve to unseat, release air pressure and give an audible alert to the operator. The safety valve is installed in the cylinder head safety valve port, directly connected to the cylinder head discharge port."

    I checked the lines and it doesn't seem like anything is clogged and not trying to be a pessimist and believe my compressor is going bad I thought I might ask around here.

    Any and all help is appreciated, Thanks in advance.
     
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  3. SWM_TECH

    SWM_TECH Light Load Member

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    Apr 15, 2018
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    Sometimes it is helpful in diagnosing air compressor issues and leaks to supply truck with external air so you can hear and identify leaks without the noise of engine running. Also, splitting the system like at the air compressor discharge line can be helpful in diagnosing leaks. In the past was trying to find out why a truck was cycling air compressor so often and in that case I split system and found the compressor head was leaking and not the signal line.
     
    Rideandrepair and J3DIKing Thank this.
  4. J3DIKing

    J3DIKing Bobtail Member

    11
    2
    Nov 13, 2023
    0
    I was recently told something similar,
    I’d have to see if I can get access to a compressor. I appreciate your input.
     
  5. Rideandrepair

    Rideandrepair Road Train Member

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    Aug 8, 2015
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    Sometimes the safety valves leak. Normal pop off pressure is pretty high. I can’t remember exactly, but higher than I expected. Maybe 200 or more? It will keep the compressor head gasket from blowing if there’s a blockage. You didn’t mention if it’s building up pressure like it’s supposed to. If the safety valves leaking, not letting it build enough pressure, it won’t pop off. What about setting the new governor? Sometimes the factory settings are off, and if needs adjusting. You mention it’s only when idling. If so, it should work correctly when idling at high RPMs, equivalent to RPMs while Driving. Try idling it up over 1100-1400, see it if pops off. If so, The leaking safety valve itself may be the cause. Could also be any leak between the compressor and dryer.
     
    Last edited: Dec 4, 2023
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